Millions visit the website each year to keep up with Santa's movements.

The tracker is a mammoth effort and relies on volunteers and donations from corporations, including computer servers and video-imaging companies.

The tracking tradition began because of a mistake in an advertisement for US department store Sears Roebuck. Instead of showing the phone number for Santa, a number for the defence command was printed.

As for that age-old vexing question of how Santa gets to each house in just one night, the command says that if Santa worked within the limits of standard time, he could only be in each home for three ten-thousandths of a second.

"Santa Claus is more than 16 centuries old, yet he does not appear to age at all," the command explains on its Santa tracker website.

"This is our biggest clue that he does not work within time as we know it. His whole trip may appear to us as taking only 24 hours, but to Santa it may last days, weeks or even months in standard time!

"Santa would never rush the important job of distributing presents to children and spreading holiday cheer to everyone, so the only logical conclusion is that Santa functions within a different time-space continuum than the rest of us. Santa is a true mystery to us all!"